Wow Jon that casing looks great! As you say, better than the PSI version..... I must admit i'm very tempted to swap out the PSI one for one of these
I actually think £40 sounds reasonable especially for something that is virtually a one-off... yes the PSI one was a bit cheaper, but by the time it was posted it would have been nearing the £40 mark.
With regard to the design of this new casing it would be nice to have a locating 'lip' where the casings mate together to align all the gears accurately & keep out dirt (like the original XXX box)... but I understand this adds more complexity & cost to these parts.
On a side-note - my PSI gearbox has done about 5-6 meetings now & it seems to be holding up ok so far. The layshaft hole is not quite central to the hole in the motor mount but I think this is done to squeeze in the extra gear. My main concern though is the fact that due to shaving down the mounting face for the motor plate it has left the plastic very thin where the layshaft bearing fits.